This invention relates to the production of stable vanadium tetrachloride. More particularly, this invention relates to the use of phosphorous trichloride to increase the shelf life of vanadium tetrachloride.
Vanadium tetrachloride is a well-known compound useful in industry as a catalyst to produce polyolefins such as polypropylene; synthetic rubbers; etc. It is also used as an intermediate for the preparation of vanadium trichloride, vanadium dichloride and organovanadium compounds.
Various processes for producing vanadium tetrachloride have been described in the prior art. Thus Chem. Abst. 64: 13727h (1965); and Chem Abst. 83: 45404q (1975) both describe the preparation of vanadium tetrachloride by chlorination of its oxytrichloride. U.S. Pat. No. 3,128,150 discloses that the conversion of vanadium oxytrichloride to vanadium chloride by chlorination in a carbon bed can be improved by preconditioning the carbon by heating to at least 200.degree. C. and passing chlorine through the carbon until the off-gas from the carbon is essentially chlorine.
The chlorination of vanadium containing materials to recover vanadium and vanadium chlorides has also been described. Thus, U.S. Pat. No. 1,779,856 discloses chlorination of an aqueous pulp of vanadium containing ores to solubilize the vanadium, thus producing a mixture of vanadium salts including vanadium oxychlorides, vanadium oxides, vanadium sulphate or vanadium chloride. The chlorination of crude residues to recover vanadium is described in U.S. Pat. No. 3,384,448; the process involves pre-treatment of the residue with an organic solvent. U.S. Pat. No. 3,775,547 describes the chlorination of vanadium oxides in the presence of carbon to provide vanadium chlorides and/or oxychlorides in a tube reactor lined with a specific heat-hardened product produced from corundum and a binder. A particular apparatus for producing vanadium chlorides from vanadium oxides is described in U.S. Pat. No. 3,895,097.
Vanadium tetrachloride has also been produced by the reaction of vanadium oxytrichloride with aromatic compounds containing a trichloromethyl group while introducing elemental chlorine into the reaction mixture; this procedure is described in U.S. Pat. No. 3,494,728.
However, regardless of the method of preparation, vanadium tetrachloride is known to be unstable, decomposing slowing to vanadium trichloride and chlorine at temperatures below 63.degree. C.